First, let me say that a picture would help. I don't know what you mean by a 'ramp', and a picture of what you are considering would help clear that up. Generally, you want a fairing around the block, rounded on the leading edge and gradually tapering to the fuselage on the trailing edge. Don't tell me that you want a picture. Think about the shape of wheel pants.

As Bruce recommended, Xfoil is probably about the best you will do for predicting where separation or transition to turbulence will occur, under a particular set of conditions, for a shape like an airfoil. For something other than an airfoil, like a block, sharp edges are always likely candidates for separation points.

banktoturn